Hollow, composite dowel bar assemblies, associated fabrication methodology, and apparatus

ABSTRACT

Hollow composite dowel bar assemblies, their manufacture, and apparatus for manufacture. The dowel bar assemblies may include an elongate and hollow core, a protective jacket coating at least the sidewall exterior of the core, and a sealing structure coupled with each end of the combined core and jacket, that are configured to protect the core from the environment.

CROSS-REFERENCES

This application is a continuation of U.S. patent application Ser. No.15/710,766 filed Sep. 20, 2017, which claims priority from U.S.Provisional Patent Application Ser. No. 62/397,320, filed Sep. 20, 2016.The complete disclosures of each application are hereby incorporated byreference in their entireties for all purposes.

The following related applications and materials are incorporatedherein, in their entireties, for all purposes: U.S. ProvisionalApplication No. 61/595,042, U.S. Patent Publication No. 2013/0202355,U.S. Pat. No. 8,591,139, U.S. Patent Publication No. 2016/0076249, andU.S. Patent Publication No. US 2017/0058463.

FIELD

This disclosure relates to dowel bars for use in concrete structures.More specifically, this disclosure relates to hollow dowel barassemblies that incorporate composite materials, apparatus formanufacturing the hollow dowel bar assemblies, and methods ofmanufacturing the hollow dowel bar assemblies.

BACKGROUND

Dowel bars are ubiquitous in concrete highway construction. They aretypically elongate, cylindrical, high-shear-strength, smooth-exteriorrods formed of conventional structural steel. Dowel bars may be employedin multiple numbers, for example at 1-foot lateral-spacing intervals, asshear-bridging, slab-to-slab load-transfer components at the jointswhich exists between adjacent, travel-direction-oriented, highway slabsformed of poured concrete.

When properly installed, dowel bars provide appropriate load-transfershear strength between adjacent slabs while at the same time (a)accommodating slab expansion and contraction (with slight, butrecurrent, slab-joint openings and closings) due to ambient thermalchanges, and additionally (b) minimizing the phenomenon known as slabfaulting at the joints between adjacent slabs. Dowel bars may also beuseful when employed for highway retrofit processes, such as to addresscracks or other flaws in an existing concrete highway.

One limitation of existing dowel bar designs is the shortening of thefunctional lifetime of the dowel bar due to corrosion. A zinc coatingmay be employed as a corrosion-accepting, sacrificial layer over steel,inhibiting steel corrosion. Unfortunately, the role of the zinc coatingas a sacrificial anode typically results in the zinc surface becomingextremely roughly surface-textured, which interferes with the desiredcapability of a dowel bar to offer smooth-outside-surface slidingcontact with surrounding concrete in order to accommodatetemperature-related expansion and contraction of concrete slabs.

Dowel bars composed of non-corrosive materials have been proposed andtried, but typically fail to provide adequate shear strength or loadtransfer efficiencies, and thus do not function well as comparablyrobust, slab-to-slab load transfer devices. Attempts to compensate forthe relative lack of shear strength and/or load transfer efficiency haveemployed greater numbers and/or closer spacing of the dowel bars,thereby increasing overall project expenses.

What is needed is a dowel bar assembly that minimizes material costs butprovides comparable, or enhanced, load transfer efficiency versus solidsteel dowel bars, while still providing sufficient shear strength andcorrosion resistance as well as permitting adequately low resistance tosliding contact with the surrounding concrete.

SUMMARY

This disclosure relates to dowel bar assemblies that incorporate bothcomposite materials and a hollow internal core, including theirmanufacture, and the apparatus for manufacturing the assemblies.Although the disclosed dowel bar assemblies possess many advantages whenused to stabilize and reinforce concrete structures, they may beparticularly well-suited for use in concrete highways.

In some aspects, the disclosure may provide dowel bar assemblies thatmay include an elongate hollow core, a protective jacket coating atleast the sidewall exterior of the core, and a sealing structure coupledwith each end of the combined core and jacket, wherein the sealingstructures are configured to protect the core.

In some aspects, the disclosure may provide a method of manufacturing adowel bar, that may include preparing an elongate hollow core precursor;coating at least a sidewall exterior of the core precursor with aprotective jacket, cross-cutting the jacketed core precursor intosegments having a desired length, and capping each end of the coresegments with a sealing structure.

In some aspects, the disclosure may provide an apparatus for formingelongate hollow dowel bar assemblies, that may include an advancingmechanism configured to advance an extended hollow core precursor; acore heater, configured to receive and heat the core precursor; a jacketapplicator, configured to apply reinforcing fibers and a curable resinto an exterior of the core precursor; a curing apparatus, configured tocure the curable resin; a pultrusion puller, configured to pull thecoated core precursor through the curing apparatus to produce a jacketedcore precursor; and a crosscutting mechanism configured to cut thejacketed core precursor into segments having a desired length.

The features, functions, and advantages of the disclosed dowel rodassemblies, manufacturing methods, and apparatus may be achievedindependently in various aspects of the present disclosure, or may becombined in yet other aspects further details of which can be seen withreference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a semi-schematic view of an illustrative dowel bar assemblyaccording to the present disclosure.

FIG. 2 is a semi-schematic view of an alternative illustrative dowel barassembly according to the present disclosure.

FIG. 3 is a cross-sectional view of dowel bar assembly 10, taken at alocation intermediate to the two end sealing structures 18 shown inFIGS. 1 and 2.

FIG. 4 is an enlarged-scale, fragmentary, side elevation of dowel barassembly 10 of FIG. 2, with portions broken away to illustrate detailsof internal construction.

FIG. 5 is an even larger-scale, fragmentary illustration of the sidewallof dowel bar assembly 10 of FIG. 2, focusing on the region in FIG. 3which is embraced by the curved arrows shown at 5-5.

FIG. 6 is a schematic and fragmentary side elevation view of anapparatus for the pultrusion-based manufacture of the disclosedcomposite-material hollow dowel bar assemblies, such as that pictured inFIGS. 1 and 2.

FIG. 7 is a block/schematic diagram illustrating a portion of amanufacturing process of the dowel bar assemblies of FIGS. 1 and 2.

FIG. 8 is a block/schematic diagram illustrating an additional portionof the manufacturing process of FIG. 7.

FIG. 9 is a flowchart illustrating a method of manufacturing a dowel barassembly, according to an illustrative embodiment of the disclosure.

Components, structures and positional relationships between elementspresented in FIGS. 1-6, inclusive, are depicted so as to more clearlyexplicate the disclosed elements, and thus are not necessarily drawn toscale.

DESCRIPTION Overview

Various embodiments of a dowel bar assembly that includes a hollow core,and associated fabrication methods and apparatus, are described belowand illustrated in the associated drawings. Unless otherwise specified,the hollow dowel bar assembly and/or its various components may, but arenot required to, contain at least one of the structure, components,functionality, and/or variations described, illustrated, and/orincorporated herein. Furthermore, the structures, components,functionalities, and/or variations described, illustrated, and/orincorporated herein in connection with the present teachings may, butare not required to, be included in other similar apparatuses. Thefollowing description of various embodiments is merely exemplary innature and is in no way intended to limit the disclosure, itsapplication, or uses. Additionally, the advantages provided by theembodiments, as described below, are illustrative in nature and not allembodiments provide the same advantages or the same degree ofadvantages.

Although the dowel bar assemblies of the present disclosure may beutilized to confer strength and durability to any of a number ofconcrete structures, or even other types of construction projects, thedowel bar assembles are particularly useful when installed in ahigh-performance concrete highway in such a manner that theyinterconnect adjacent concrete slabs, thereby helping to transfervertical loads between slabs. Typically, such installation would includemultiple dowel bar assemblies, laterally spaced, and disposed at about1-foot lateral intervals along the joints between concrete slabs.

FIG. 1 is a semi-schematic view of an illustrative dowel bar assemblyaccording to the present disclosure, generally indicated at 10. Thecomponents of dowel bar assembly 10 include an elongate, cylindrical,and hollow core 12; a coating or jacket 14 that is applied to andprotects the outer surface, or exterior sidewall 16, of core 12; and twosealing structures 18 that are coupled to each end of jacket 14 toprotect core 12 by sealing it from exposure to moisture.

FIG. 2 is a semi-schematic view of an alternative illustrative dowel barassembly 10 according to the present disclosure, including an elongate,cylindrical, and hollow core 12; a jacket 14 surrounding the exteriorsidewall of core 12, and two sealing structures 18 that are coupled toeach end of jacket 14, to protect core 12 from exposure to moisture.

FIG. 3 is a cross-sectional view of dowel bar 10, taken at a locationintermediate to the two end plug blanks 18 shown in FIG. 1. As core 12may be a hollow tube having a central passage 13, the core may have aninner surface 15 disposed at an inner core Ri as measured from the longaxis 10 a of the dowel bar. Core 12 may have an outer surface 16 towhich outer sleeve 14 is bonded. Though core 12 is shown in FIG. 2 ashaving a circular cross-section, any shape is possible for thecross-section of core 12, end plug blanks 18, and dowel bar assembly 10.

While it should be appreciated that dowel bar assemblies of varyingdimensions may be required for a particular application, the dowel barassemblies of the present disclosure may typically exhibit an overalllength (D1 in FIG. 4) of about 12 to about 24 inches, and an outsidediameter (D2 in FIG. 4) of about 1 to about 2½ inches. More typically,an exemplary dowel bar may have a length of about 16 to about 18 inchesand an outside diameter of about 1½ to about 2 inches. Preferably, thedowel bar assembly has an outer diameter of about 1.7 inches.

Core

Although any number of materials may be used to form the elongate andcylindrical core 12, preferably core 12 is manufactured from a materialhaving a capacity for efficient load transfer, such that afterinstallation in a joint between concrete slabs the dowel bar assembly 10is capable of efficiently transmitting vertically-applied stresses dueto transient loading across the joint to an adjacent concrete slab.Additionally, the core 12 should be selected to exhibit adequate shearstrength on the materials encapsulating it, particularly when installedinto a poured concrete structure. For at least these reasons core 12 maytypically be prepared using a conventional structural steel formulation.In one aspect of the present disclosure, the core is made using ASTM 615Grade 60 carbon steel.

It was determined that the use of a hollow cylindrical core in place ofa solid cylindrical core as described in U.S. Pat. No. 8,591,139, mayresult in dowel bar assemblies that are substantially lighter than thosehaving solid steel cores. Furthermore, the use of a hollow-core dowelbar assembly results in enhanced load transfer efficiency and reducedcorner pressure. In one embodiment, installation of hollow dowel barassemblies having an outer diameter of 1.7 inches, compared to soliddowel bars having a diameter of 1.5 inches, results in load bearingstress being reduced by 25% and corner pressure being reduced by 27%.The resulting hollow dowel bar assemblies therefore provide equivalentor significantly improved performance with a significant savings in bothmaterials and transportation costs.

Where core 12 extends to the ends of jacket 14 (as shown in FIG. 1), thelength of core 12 is necessarily substantially equivalent to the lengthof the jacket, or a length (D1 in FIG. 4) of about 12 to about 24inches. Where core 12 is shorter in overall length than jacket 14 (asshown in FIG. 2), the ends 12 b of core 12 may be recessed from one orboth ends 19 of jacket 14 by about ¼ inch to about 1 inch at each end,or overall ½ inch to 2 inches shorter overall where core 12 is recessedat both ends.

It should be appreciated that the inner diameter of jacket 14 isnecessarily related to the outer diameter of hollow core 12 (D4 in FIG.4), and is typically substantially equal to the outer diameter of core12, which is about 0.8 to about 2.4 inches. Preferably, core 12 is about16 to about 18 inches long and has an outside diameter of about 1.5inches, more preferably core 12 has an outside diameter of 1.625 inches.

The wall thickness 20 of core 12 (see FIG. 3) may be about 1/16 inch toabout ¼ inch, and is more typically about ⅛ inch.

Jacket

Protective jacket coating 14 provides multiple advantageous propertiesto the dowel assemblies of the disclosure. Jacket 14 substantiallycompletely covers the exterior sidewall of core 12, and in conjunctionwith the sealing structures 18 capping the ends of the dowel assembly10, protects core 12 from exposure to potential corrosion-causingelements, particularly moisture. In addition, however, by carefulselection of the materials used to form jacket 14, the coating can alsoenhance the strength of the resulting dowel assembly, and function as a“bond breaker” when the dowel bar assembly is set into concrete.

A bond breaker is a layer of a material that is applied to a solid thatis being encapsulated in a matrix in order to prevent adhesive bondingbetween the solid and the matrix material. For dowel bar assemblies, theapplication of a bond breaker facilitates the ability of the dowel barto slide within the concrete matrix, thereby accommodating bothtemperature-related expansion and contraction, and the response of theconcrete to high impulse and/or transient loading. This helps to preventformation of cracks within the concrete.

Although a variety of substances may be applied to dowel bars tofunction as bond breakers, most are applied in the form of a liquid orsemi-liquid, a spray, or a tape wrapping. By encapsulating dowel barassembly 10 with an appropriately selected material, the dowel barassemblies of the present disclosure exhibit minimal adhesion with thesurrounding concrete without requiring the application of an additionalbond breaker material. The efficacy of the protective jacket material ineliminating the need for a bond breaker material may be evaluated bymeasuring the pullout stress of the dowel bar assembly. A measuredpullout stress of less than 60 psi when tested in accordance with AASHTOT253 indicates that the dowel bar assembly will function without theneed of an applied bond breaker material.

The protective jacket 14 may comprise a curable plastic resin. Theplastic resin may be selected to be cured via the addition of anappropriate curing agent or catalyst, or the plastic resin may be athermoset plastic. Typically, the plastic is a thermoset plastic that isselected for resilience, durability, and stability. Plastic resinmaterials that may be useful for forming jacket 14 include conventionalurethane-modified thermoset vinylester resin material, such as Dion31038-00, made by Reichhold Inc. in Durham, N.C., USA.

The plastic resin used to form jacket 14 may additionally include one ormore additives intended to confer resistance to photodegradation of theresin. That is, additives may be added to the plastic resin that mayhelp screen the plastic resin from exposure to UV light, potentiallypreventing or minimizing damage to the dowel bar assemblies that mayotherwise occur when they are exposed to direct sunlight.

The properties of jacket 14 may be substantially improved by theincorporation of fibers within the plastic resin matrix. Such reinforcedplastics may generally be known as composite materials, as the materialcombines two (or more) constituents (the fibers and the surroundingmatrix) to create a material with substantially different propertiesthan either constituent material. In particular, by incorporating fiberswithin the plastic resin matrix, jacket 14 may confer substantiallyimproved load transfer efficiency, strength, and shear resistance ontothe resulting dowel bar assembly.

When present, the fibers used to reinforce jacket 14 may be uniform ornon-uniform, and may have similar or different compositions. In someaspects, the fibers may be polymer-based, including polyester polymerssuch as polyethylene, or polyamide polymers such as poly-aramid, amongothers. Alternatively or in addition, the fibers may be derived fromnatural sources, such as plants, for example flax, hemp, or agave, amongothers. The fibers may be or include glass fibers, including E-glass,E-CR-glass, S-glass, basalt, or fused quartz fibers. The fibers mayinclude boron fibers or boron nitride fibers. In one illustrativeexample the fibers may include carbon fibers, such as graphite fibers.The fibers may include woven fibers or non-woven fibers.

Additionally, the fibers used to form jacket 14 may be discrete fibershaving little or no arranged orientation in the matrix, or they may belonger fibers that are applied with a shared orientation or architecturethat provides advantageous qualities. In a particular aspect of thepresent disclosure, the fibers used to form jacket 14 may be appliedcontinuously, for example by being wound onto the core 12 with anappropriate plastic resin in a desired pattern, followed by pultrusionas will be discussed below.

In one aspect of the disclosure, jacket 14 may include up to threedifferent, or differentiated, examples of reinforcing fibers embedded ina plastic matrix. The reinforcing fibers may be made of glass, and morepreferably E-glass (alumino-borosilicate glass with less than 1 w/walkali oxides). Alternatively, or in addition, the reinforcing fibersmay be made from a thermoplastic polymer.

Selected examples of reinforcing fibers may include (1) glass-fiberroving, (2) glass-fiber mat, and (3) glass-fiber veil materials. Inglass-fiber roving materials, the glass fibers of the matrix areelongate and may be oriented substantially parallel to the longitudinalaxis 10 a of the dowel bar assembly 10. In glass fiber mat materials,the glass fibers are utilized in the form of a sheet or mat havingrandomly oriented fibers. In glass fiber veil materials, the sheet ormat includes more evenly dispersed glass fibers that may exhibit somedegree of orientation within the sheet. Typically, the composition ofjacket 14 is selected so that the glass fibers incorporated in thejacket make up about 60% by weight of the entire jacket.

In the case of fiber veil materials, the reinforcing fibers may includea thermoplastic polymer, such as thermoplastic polyester. Suitable spunpolyester veil materials may be commercially obtained under thetradename REEMAY.

Each type of the glass fiber reinforcing materials may be obtainedcommercially in a wide variety of choices, sizes, and othercharacteristics, and may freely be selected for use in the manufactureof the disclosed dowel bar assemblies. Representatively,fiber-reinforcing materials which have been found to be well-suited foruse in many high-performance highways include: (a), for mat material,continuous-strand glass fiber products made and offered by Owens Corningin Pennsylvania, USA; (b), for roving material, a selection drawn fromthe products also made by Owens Corning; and (c), for veil material,what are referred to respectively as “tissue veil” and “veil cloth”products made available by Freudenberg Nonwovens in Durham, N.C., andXamax in Seymour, Conn.

An illustrative embodiment of a dowel bar assembly 10 according to thepresent disclosure is depicted in FIGS. 4 and 5. As shown, jacket 14includes a total of four concentric layers that incorporate reinforcingfibers, shown at 22, 24, 26, and 28.

Layer 22, which appears as a wavy line in FIG. 4, may include a glassfiber mat material. Layer 24, which appears as a thickened, straightline in FIG. 4, may include a glass fiber roving material. Layer 26,which also appears as a wavy line in FIG. 4, may include a glass-fibermat material. And, layer 28, which appears as a thin, straight,dash-double-dot line in FIG. 4, may include glass-fiber veil material.

Without wishing to be bound by theory, the incorporation of fiber matmaterials having randomly oriented fibers into jacket 14 may help toreduce the tendency of the plastic material of the jacket from splittingor cracking longitudinally when under stress. Alternatively, or inaddition, one or more applications of fiber mat may be replaced bywinding fibers onto the core at an off-axis angle to provide enhancedmechanical toughness and impact resistance. More preferably, fiber maybe wound onto the core at two different and complementary off-axisangles, to further increase stiffness and resistance to splitting. Inone embodiment of the disclosure, two sets of fibers may be wound ontothe core to form jacket 14 at complementary angles ranging from +30° and−30° to angles of +60° and −60°. In a preferred embodiment, two sets offibers are wound into the jacket at off-axis angles of +45° and −45°,respectively, from the longitudinal axis 10 a.

It should be appreciated that jacket 14 may include any usefulcombination of reinforcing fibers, types of reinforcing fibers, anddistribution of reinforcing fibers within the plastic resin matrixforming the jacket, including a jacket that includes a single discretelayer incorporating a type of reinforcing fiber. Alternatively, or inaddition, any combination of two or more of the representative layers22, 24, 26, and 28 may be disposed within jacket 14 in an alternativelayer order. In one particular alternative embodiment of the dowel barassembly of the present disclosure, jacket 14 may include only three ofthe four layers depicted in FIGS. 3 and 4: a mat-material layer 22, aroving-material layer 24 disposed outwardly of layer 22, and aveil-material layer 28 disposed outwardly of roving-material layer 24.

Sealing Structures

Each dowel bar assembly 10 includes sealing structures 18 that areconfigured to substantially seal the open ends of the combined core 12and jacket 14 so as to help protect the core from exposure to moisture,which may lead to corrosion. Any shape or composition of sealingstructure that adequately protects core 12 from exposure to moistureand/or other corrosive materials is a satisfactory sealing structure forthe purposes of the present disclosure.

Where core 12 and jacket 14 have substantially equal lengths, as shownin FIG. 1, the ends of the dowel bar assembly 10 may be sealed by theapplication of insertable caps 30. Each cap 30 includes an insertportion 32 and a capping portion 34. Insert portion 32 is configured tobe inserted into the open end of combined core and jacket 36, i.e., intothe hollow interior of core 12. Insert portion 32 of cap 30 should beshaped so as to create a moisture-proof seal when inserted into thehollow interior 13 of core 12. For example, as shown in FIG. 1, insertportion 32 of cap 30 may include one or more protrusions 38, such asflange structures or ribs, that can enhance the frictional fit betweenthe insert portion and the core interior. Alternately or additionally,cap 30 may be screwed into the end of core 12 if one or both of insertportion 32 and inner surface 15 includes complementary threads. Anystructure that serves a similar purpose may be used in place of, or inaddition to, the depicted protrusions 38.

It should be appreciated that capping portion 34 may have acircumference substantially equal to the outside diameter of jacket 14,so as to completely protect the ends of the combined jacket and core 36.Alternatively, the circumference of capping portion 30 may be largeenough to substantially cover the exposed end of core 12, i.e.,substantially equal to the outside diameter of core 12 (D4) so that thecore material is protected from the environment.

Alternatively, or in addition, cap 30 may be sealed to the ends of thecore 12 and/or jacket 14 using a sealant material, such as a caulk, anadhesive, or other material. While curable materials may be used toenhance a permanent seal between the cap and the dowel bar assembly,non-curable materials may also be used, such as TEFLON tape, plumber'sgrease, and the like.

Cap 30 may be made of any appropriate material or combination ofmaterials, for example rubber, plastic, or any other material capable ofwithstanding the environment within a concrete structure. Caps 30 may beprepared for example by injection molding. A variety of such insertablecaps or plugs are commercially available.

In an alternative embodiment of the present disclosure, the core 12 doesnot extend fully to the ends of the jacket 14, and the ends of thejacket 14 are sealed with end plugs 40, as described in U.S. Pat. No.8,591,139. Such end plugs 40 may include elongate roving reinforcingfibers in a plastic resin matrix. The reinforcing fibers may bedistributed throughout the plastic resin matrix of the plugs, and may beoriented so as to extend substantially parallel to the longitudinal axisof the dowel bar assembly 10 a.

As will be discussed below, in this embodiment the jacket 14 may beformed via pultrusion over an alternating sequence of core segments andplug segments, followed by cross-cutting through the plug segments toform the dowel bar assembly. By manufacturing the jacket 14 in this way,the jacket material is not subjected to contact with any sharp-edged,high-stress, surface discontinuity regions within the dowel barassembly.

Where the sealing structures 18 are end plugs 40, they may be fabricatedfrom a conventional thermoset polyester material made by RazorComposites in Baraboo, Wis. Sleeve end plugs 40 may have a length (D6 inFIG. 3) of about 1 inches, and a circular cross section or diametersubstantially equal to the outer diameter of core 12, and thus the innerdiameter of jacket 14.

Manufacturing Apparatus

The dowel bar assemblies 10 of the present disclosure may be fabricatedusing a pultrusion apparatus for example as described in U.S. Pat. No.8,591,139 and depicted semi-schematically in FIG. 6.

FIG. 6 illustrates, at 68, an apparatus for implementing thepultrusion-based manufacture of dowel bar assemblies of the presentinvention.

Progressing from left to right, i.e., from upstream to downstream endsof apparatus 48, across FIG. 6, apparatus 48 includes (1) an advancingmechanism, or core-train pusher, 52, simply represented by a darkenedarrow whose arrowhead points in the direction of processing flow throughapparatus 48, (2) a core-train formation, or forming, station 54, (3) acore heater H₁ which is disposed within station 54 and designed to heatcores 12, as will be further explained, to a temperature of about 150°F. before the actual process of jacket formation via pultrusion begins,(4) a reinforcing fiber supply station 56 which, represented necessarilyjust in the plane of FIG. 6 (i.e., on one side only ofpultrusion-formation axis 48 a), is seen to include herein four,reinforcing-fiber-material distributing devices that are illustrated asrotary fiber-delivery spools 58, 60, 62, 64—devices that are merelyrepresentative of any number of variations in user-selectable,conventional structures designed to pay out, respectively, elongate,fiber-material runs, such as those appearing as straight, angularlyinclined lines in FIG. 6, of for example glass fiber mat material 22,glass fiber roving material 24, glass fiber mat material 26, and glassfiber veil material 28, (5) a resin fiber bathing, or resin bathing,station 65, and a fiber guide station 66 which, like fiber supplystation 56, are respectively pictured necessarily just in the plane ofFIG. 6 only on one side of axis 48 a, (6) another heater, H₂, (7) aconventional, and appropriately sized pultrusion die 68, the inside ofwhich is heated to a temperature of about 280° F. by heater H₂(pultrusion die 68 is depicted herein with a length of about 5- to6-feet, and an internal, elongate, cylindrical pultrusion channel with adiameter of about 1½-inches), (8) a conventional, power-driven,pultrusion puller of any suitable design, such as a crawler treaddesign, represented simply by a darkened arrow 70, operable herein toestablish a pultrusion throughput speed of about 3 to about 7feet-per-minute, more preferably about 5 feet-per-minute, and (9) asuitable crosscutting mechanism 72 which is employed to cross cut whatis referred to herein as a pultrusion result, intermediate, dowel barproduct, such as that designated 74 in FIG. 6, that is emerging from die68. A fragmentary, end portion of a finished, cut-separated dowel-bar 10is pictured to the right of cutter 72.

It should be understood that, while four, fiber-delivery spools(devices) have been illustrated in FIG. 6 in order to relate to adiscussion regarding the delivery of fiber-reinforcing materialssuitable to create four layers within a jacket 14, in the context offabricating a sleeve having only three layers within it, only three suchdelivery spools (devices) would be required, and, in terms of what isillustrated in FIG. 6, these three spools would include spools 58, 60and 64.

Further discussing what has just been described respecting FIG. 6, thethree, upstream processing stations, and the associated structuresillustrated therein, which are involved with (1) supplying, i.e., payingout, from suitable delivery devices, such as the representativelypictured delivery spools, elongate runs of the several different kindsof reinforcing fiber materials, (2) for bathing the thesereinforcing-fiber-material runs en route to the pultrusion die with theappropriate plastic resin, and (3) for guiding the bathed fiber materialruns into the infeed, upstream end of the pultrusion die, mustnecessarily be constructed, and this may be done in entirelyconventional, user-chooseable manners, so as to be distributedrelatively evenly around, i.e. circumferentially around,pultrusion-forming axis 48 a so that a sleeve or jacket 14 ultimatelybecomes pultrusion-formed uniformly circumferentially around a core 12.Just how this circumferential distribution of paying out, bathing andguiding equipment is organized, and what particular type of suchequipment is employed, is entirely a matter of user/designer choice.

Located preferably adjacent both (1) the upstream, or infeed, and (2)the downstream, or discharge, ends of apparatus 48, are suitabletrack-like, such as trough-like, and preferably, though not necessarily,stationary, support structures, not illustrated herein, that provideappropriate, underlying support (a), adjacent the upstream end of theapparatus for what will shortly be described as a stream of elementsthat make up a pre-pultrusion core-train of dowel-bar central elements(i.e., endo-abutting, longitudinally alternating cores and end-plugblanks) that are to be fed into die 68 for pultrusion forming of jacketstructure 14, (b), adjacent the downstream end of the apparatus, and ofdie 68, for the emerging intermediate, pultrusion-result, dowel-barproduct, such as that shown at 74, and (c), beyond cross-cutter 72, forthe finished and thereafter separated dowel bars 10. Other modes, etc.,of underlying “component-throughput-transport” support may, of course,be implemented.

While the process of sleeve formation herein is clearly apultrusion-based process, at the extreme upstream end of apparatus,there are engaged herein, as will now be described, upstream, coreforming and core advancing operational stages that relate to the neededformation, and then the downstream transport, of the componentscorresponding to the horizontal, linear feed entering station 54 forfeeding from that station toward stations 65, 66, and pultrusion die 68.

Where the desired dowel bar assembly corresponds to the dowel barassembly of FIG. 1, that is where the core 12 extends substantially thelength of jacket 14, the horizontal, linear feed entering station 54 ismade up on a continuous and tubular core precursor, such as acylindrical steel tube. However, the apparatus of FIG. 6 is depicted asfabricating a desired dowel bar assembly that corresponds to the dowelbar assembly of FIG. 2, where jacket 14 extends beyond the length ofcore 12 and the sealing structures 18 that are used are end plugs 40fitting within jacket 14. As shown in FIG. 6, the horizontal, linearfeed being advanced by mechanism 52 is a continuous train ofendo-abutting, longitudinally alternating, elongate, cylindrical, highload transfer efficiency, high-shear-strength, steel cores 12, andshorter, elongate, cylindrical and matching-cross-section, plastic-resinand fiber-reinforced, pre-pultruded sleeve end-plug blanks 78. One suchend-plug blanks is disposed just upstream from die 68, and the other isdisposed within the die. As will become apparent shortly, each end-plugblank has a length which is about twice that of the desired finished endplug 40, and in one aspect the length may be about 2 inches.

Considering now the overall dowel-bar formation pultrusion processproposed by the present invention, as the linear core precursor, or coretrain, including endo-abutting, longitudinally alternating cores andend-plug blanks, is suitably formed along a line in forming station 54.Within this station, as the formed core train is moved by pusher 52toward the pultrusion die, and by appropriately timed and stagedoperation of previously described heater H₁, which may take any suitableform of a heater selected by the user, and which may conveniently andconventionally be operated under the control of a suitably programmed,digital computer (not part of the present invention), the steel cores inthe train are preferably heated, as mentioned earlier herein, to atemperature of about 150° F. Such heating is preferably done in order toprevent the cores, during processing within pultrusion die 68, fromacting as undesired heat sinks which could retard, and perhaps interferewith, appropriate curing of the resin which coats the fiber reinforcingmaterials within the die.

The formed core precursor, with either its extended steel core materialor alternating core segments and end-plug precursors, is moved from theforming station toward and into the die by advancing mechanism 52, whichis operated in any appropriate fashion, entirely selectable by the user,to shift the core precursor components at an appropriate rate toward andinto the pultrusion die, and in a manner so as to accommodate, as far asthe operational limitations of the pultrusion die may be considered, asubstantially steady and effectively continuous stream of freshlydie-introduced core precursor.

There are many conventional ways that a pusher, such as schematicallyillustrated pusher 52, may be constructed and operated so as (1) topermit easy, essentially continuous assembly in station 54 of aprogressively formed core precursor, and (2), at appropriate moments topush the precursor assembly so that the pultrusion die will experience acontinuity inflow of core precursor. Those skilled in the art willrecognize that once the substantially “endless” core precursor, or coretrain, is pushed to an appropriate location along pultrusion-formationaxis 48 a, is sufficiently disposed within the pultrusion die, andspecifically sufficiently contained therewithin so that resin-coated,fiber reinforcing, sleeve material has begun to stick to the core train,the downstream operation of puller 60 “takes over” in conventionalpultrusion fashion, and thereafter functions to continuously drive thedownstream-directed, flowing motion of all within the die.

Where the core precursor assembly includes alternating cores andend-plug blanks, proper endo abutment between the cores and end-plugblanks in the assembly during the core train forming process, and theassociated moving of a formed core train into die 68, may depend uponthe opposite ends of the alternating cores and end-plug blanks lyingcorrectly in parallel planes that are disposed normal to the respectivelong axes of these components.

While the core precursor is being advanced, the desired number ofreinforcing fiber materials such as 22, 24, 26, and 28 is applied in acontinuous manner to the core precursor, as shown in FIG. 6. Thereinforcing fiber materials are (1) paid out from the spools in fibersupply station 56, (2) are led through resin bathing station 65 whereinthey are bathed in, and wetted with, the selected plastic resin, andthereafter (3) guided through, and by, guide station 66 toward and intothe intake end of pultrusion die 68, appropriately disposed,circumferentially about apparatus axis 48 a, and, of course, in theappropriate radially organized layer arrangement, which has beenmentioned earlier herein, distributed circumferentially around the nowcentrally (on axis 48 a) located core precursor so as to be arranged,within the pultrusion die, for the correct formation of a jacket 14.

If, as discussed previously, a jacket having three layers of reinforcingfibers is desired, the reinforcing fiber material may be delivered fromspools 22, 24, and 28. Alternatively, if the embodiment having fourlayers of reinforcing fibers is desired, the reinforcing fibers may bedelivered from all four, illustrated spools. Also as discussedpreviously, the number and character of the jacket layers, and thenumber of reinforcing fibers employed in the manufacture of the dowelbar assemblies, is a matter of design choice.

Within pultrusion die 68, as the through-moving core precursor and theassociated, surrounding, wetted reinforcing fiber materials pass throughthe die, an appropriate level of heat is applied by heater H₂.Typically, die 68 is heated to an internal temperature of about 280° F.This heating, coupled with the attendant contact with a moving surfacewhich occurs with the internal, cylindrical pultrusion channel withinthe die, causes the resin-coated mass of material to form appropriatelyaround the core precursor in the configuration of what is to become thesurrounding jacket 14. The heating of die 68 and the degree of internalheating is selected so that the plastic resin material is effectivelysubstantially cured. This curing is to some extent aided by heatradiated from the pre-heated steel core precursor which, because of itspre-heated condition, does not negatively act as an undesirable heatsink within the die.

It will be well understood by those skilled in the art that (1) the rateof throughput of materials established selectively in apparatus 48 inthe formation of dowel bars, (2) the selected level of internal-dieheating which is created by heater H₂, and (3) the overall length of die68, per se, are appropriately determined by the specifically chosensizes of the materials that are to be employed in the making of aparticular size and character of a dowel bar assembly 10, and inrelation to the formation curing characteristics of the chosen plasticresin material.

As has been mentioned herein, what emerges continuously duringdowel-bar-making, from the downstream, discharge end of die 68, is whathas been referred to hereinabove as an intermediate pultrusion-resultdowel-bar product (or jacketed core intermediate) as seen at 74 in FIG.6.

In an alternative aspect of the disclosure, where the reinforcing fibersare applied by winding them onto the core precursor, the resin and woundfiber layers coating the core precursor may be cured by pulling the coreprecursor through a curing oven, instead of pulling the coated coreprecursor through the heated die 68. An example of such a process isshown in FIGS. 7 and 8, and in particular at box 88 of flowchart 80.

Downstream from die 68 or an appropriate curing oven, and underappropriate operational and timing control, such as might be implementedby a suitably programmed digital computer, crosscutting mechanism 72 maybe operated to produce a cross cut in this emerging “intermediate”product, with each such cut being made at a location to generate a dowelbar assembly of the desired length.

Where the jacketed core intermediate includes alternating steel coresand end-plug precursors, the cross-cutting mechanism may be configuredto cut the intermediate at a point that is substantially exactly midwaybetween the opposite ends of each core-plug blank. Such a cross cut isshown generally at 79 in FIG. 6.

The result of this operation is, of course, separation, one afteranother, of completed jacketed core segments. Where the jacketed coresegments incorporate end-plugs, the result is a completed dowel barassembly 10. However, where the cross-cut segments are not alreadycapped by a sealing structure 18, the resulting segments may be sealedby the insertion at each end of a cap or plug 30, as discussed abovewith respect to the embodiment of FIG. 1.

Method of Manufacture

The apparatus described above lends itself to the performance of variousmethods of manufacturing dowel bar assemblies, as disclosed herein. Arepresentative method of manufacture is shown in flowchart 80 of FIG. 7,which depicts an order of manufacturing operations beginning with aninput of the linear core precursor 82 into the linear core precursorheater at 84. The heated core precursor is in passed through the windingresin/reinforcing fiber applicator at 86, and then into the curing ovenH₂ to cure the resin at 88. The wrapped or jacketed core intermediate isthen drawn through the pultrusion puller at 90, and the resultingextended jacketed core is cross-cut to the desired lengths at 92 toproduce jacketed core segments utilized to prepare the capped dowel barassemblies as represented by FIG. 1.

As shown in flowchart 100 of FIG. 8, the jacketed core segments 94 mayin turn be smoothed using a centerless sander, as shown at 102, and thensealant may be applied to the core segments at 104. The sealed coresegments may then be heated in a curing oven at 106, followed by a finalcross-cutting at 108, and installation of appropriate end caps 30 at110, to yield complete dowel bar assemblies 10 at 112.

This manufacturing scheme may be modified or varied, as is wellunderstood by one of skill in the art, without departing from the spiritof the invention. For example, for some formulations, the plastic resinapplied to the reinforcing fibers to form jacket 14 may be cured andhardened at least in part by exposure to UV radiation, rather thansolely by heating. Additionally, or in the alternative, the applicationof sealant to the core segments at 104 of flowchart 100 may include orfurther comprise the application of a UV light-protective screeningmaterial, so as to prevent or minimize exposure of the plastic resin ofjacket 14 to UV light, and thereby help prevent photodegradation, suchas may occur during storage particularly in direct sunlight.

An alternative flowchart 120 of FIG. 9, also depicts a method ofmanufacturing a dowel bar assembly that includes preparing an elongate,cylindrical and hollow core precursor at 122; coating the sidewallexterior of the core precursor with a protective jacket at 124;cross-cutting the jacketed core precursor into segments having a desiredlength at 126; and capping each end of the jacketed core segments with asealing structure at 128.

Accordingly, the present invention features a special pultrusion-basedfabrication methodology, in certain variations for creating a pair ofmodifications of important, new, advanced-performance andsignificantly-enhanced-longevity highway dowel bars. Variations andmodifications are, of course, possible which will come within the spiritof the invention, and which may well come to the minds of thosegenerally skilled in the relevant art.

Advantages, Features, Benefits

The different embodiments of the hollow dowel bars described hereinprovide several advantages over known solutions for creating a dowel barthat is light-weight and long-lived. For example, the illustrativeembodiments of the hollow dowel bars described herein allow for a morelight-weight dowel bar as compared to a solid dowel bar without acorresponding loss in load transfer efficiency. No known system ordevice can perform these functions, particularly as a composite-materialdowel bar. Thus, the illustrative embodiments described herein areparticularly useful for concrete structures. However, not allembodiments described herein provide the same advantages or the samedegree of advantage.

CONCLUSION

The disclosure set forth above may encompass multiple distinctinventions with independent utility. Although each of these inventionshas been disclosed in its preferred form(s), the specific embodimentsthereof as disclosed and illustrated herein are not to be considered ina limiting sense, because numerous variations are possible. To theextent that section headings are used within this disclosure, suchheadings are for organizational purposes only, and do not constitute acharacterization of any claimed invention. The subject matter of theinvention(s) includes all novel and nonobvious combinations andsubcombinations of the various elements, features, functions, and/orproperties disclosed herein. The following claims particularly point outcertain combinations and subcombinations regarded as novel andnonobvious. Invention(s) embodied in other combinations andsubcombinations of features, functions, elements, and/or properties maybe claimed in applications claiming priority from this or a relatedapplication. Such claims, whether directed to a different invention orto the same invention, and whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the invention(s) of the present disclosure.

1. A dowel bar assembly, comprising: an elongate hollow core; aprotective jacket coating at least a sidewall exterior of the core, andhaving a bond breaker exterior; and a sealing structure coupled witheach end of the combined core and jacket, wherein the sealing structuresare configured to protect the core.
 2. The dowel bar assembly of claim1, wherein the core includes a tube having a cross-section that iscircular, elliptical, or oval.
 3. The dowel bar assembly of claim 1,wherein the core is a hollow cylinder.
 4. The dowel bar assembly ofclaim 1, wherein the core is selected to have a high load transferefficiency.
 5. The dowel bar assembly of claim 1, wherein the core isstructural steel.
 6. The dowel bar assembly of claim 1, wherein theprotective jacket is configured to serve as a bond breaker coating forthe dowel bar assembly.
 7. The dowel bar assembly of claim 1, whereinthe protective jacket includes a plastic resin.
 8. The dowel barassembly of claim 7, wherein the plastic resin is reinforced by one ormore reinforcing fibers.
 9. The dowel bar assembly of claim 1, whereinthe protective jacket includes a fiber-reinforced plastic resin havingmultiple layers of reinforcing fibers.
 10. A method of manufacturing adowel bar, comprising: preparing an elongate hollow core precursor;coating at least a sidewall exterior of the core precursor with aprotective jacket; cross-cutting the jacketed core precursor intosegments having a desired length; and capping each end of the coresegments with a sealing structure.
 11. The method of claim 10, whereinpreparing the elongate hollow core precursor includes preparing a coreprecursor having a cross-section that is circular, elliptical, or oval.12. The method of claim 10, wherein the core precursor includes a hollowcylinder.
 13. The method of claim 10, wherein coating the core precursorwith a protective jacket includes pultrusion-forming a fiber-reinforcedplastic-resin sleeve continuously and bondedly around the core precursorto form a coated core precursor.
 14. The method of claim 13, whereinpultrusion-forming the fiber-reinforced plastic-resin sleeve includescontinuous dispensing of a reinforcing fiber; applying a curable plasticresin to the reinforcing fiber, and guiding the resin-soaked fibers intoa circumferential layer structure circumsurroundingly disposed onto anoutside surface of the core precursor.
 15. The method of claim 14,wherein pultrusion-forming the fiber-reinforced plastic-resin sleeveincludes guiding the resin-soaked fibers into a circumferential layerstructure having the fibers oriented at an off-axis angle relative to alongitudinal axis of the core precursor.
 16. The method of claim 13,wherein preparing the core precursor includes longitudinally alternatinga plurality of core segments with end-plug blanks having an outsidediameter substantially equal to the outside diameter of the coresegments; and cross-cutting the jacketed core precursor includes sawingacross the end-plug blanks so that each jacketed core segment iseffectively capped.
 17. The method of claim 13, wherein the coreprecursor includes a longitudinally extended core precursor;cross-cutting the jacketed core precursor includes sawing through thejacketed extended core precursor to yield jacketed core segments; andcapping each end of the jacketed core segments includes inserting aprotective end cap into each end of the jacketed core segment.
 18. Anapparatus for forming elongate hollow dowel bar assemblies; comprisingan advancing mechanism configured to advance an extended hollow coreprecursor; a core heater, configured to receive and heat the coreprecursor; a jacket applicator, configured to apply reinforcing fibersand a curable resin to an exterior of the core precursor; a curingapparatus, configured to cure the curable resin; a pultrusion puller,configured to pull the coated core precursor through the curingapparatus to produce a jacketed core precursor; and a crosscuttingmechanism configured to cut the jacketed core precursor into segmentshaving a desired length.
 19. The apparatus of claim 18, wherein thecuring apparatus includes a heated pultrusion die, configured to receivethe fiber- and resin-coated core precursor and cure the curable resin.20. The apparatus of claim 18, wherein the curing apparatus includes acuring oven, configured to receive the fiber- and resin-coated coreprecursor and cure the curable resin.